5. in imitation of the Hebrew בֶּטֶן, tropically, the innermost part of a man, the soul, heart, as the seat of thought, feeling, choice (Job 15:35; Job 32:18 (the Sept.γαστήρ); Proverbs 18:8 (the Sept.ψυχή); (the Sept.σπλάγχνα); Habakkuk 3:16; Sir. 19:12 Sir. 51:21): John 7:38.

Strong's Exhaustive Concordance

belly, womb.

From koilos ("hollow"); a cavity, i.e. (especially) the abdomen; by implication, the matrix; figuratively, the heart -- belly, womb.